To form a photoresist layer on a semiconductor substrate (typically prior to an implanting process and an etching process) a conventional process coats the surface of a semiconductor wafer with a photoresist material. Next, the photoresist material disposed on the surface of the wafer is masked, exposed, and developed to provide a patterned photoresist layer.
The process for coating the surface of the wafer with the photoresist material is performed in a coating device. The coating device dispenses the photoresist material onto the semiconductor wafer while concurrently rotating the wafer to uniformly coat the semiconductor wafer.
Throughout the coating process, the wafers are softly baked and then remain in the buffer unit of an interface block before being moved to an exposure device. A process for exposing the wafers in the buffer unit includes: (a) moving a top positioned wafer in a queue of the buffer unit to a wafer notch position check block by means of a wafer loader, (b) checking orientation flatness with LED sensors to detect the position of a notch during the several rotations of the wafer, (c) conveying the roughly aligned wafer to a wafer stage, and (d) precisely aligning and then performing an exposing process for the wafer on the wafer stage.
Conventionally, a method for sensing a coating failure of the semiconductor wafer is performed prior to the exposing process. This sensing method performs a statistical sample test for a few wafers in a lot or a batch by means of detecting equipment or macrography after the completion of the development process for the photoresist material on the wafer.
Photoresist coating failures may cause serious problems such as yield loss during the later implanting process and the etching process. In other words, areas having coating failures cannot provide important functions such as implant blocking mask and etch resistance mask, thereby resulting in defective chips.
Thus, the test process for developed wafers is an essential part in the formation of a photoresist layer.
However, a full inspection for all wafers may cause a decrease in productivity and throughput. As a result, instead of an inspection of all wafers, the above-described sample test is performed after the exposing process. Since, by definition, the sample test does not test all of the wafers, unsampled wafers with coating failures may remain throughout the later processes. Thus, unsampled wafers with coating defects will not be detected and will, thus, likely escape the process for stripping and re-coating the photoresist material. These defective and unrepaired wafers cause problems and may result in a severe yield loss.
Shiraishi et al., U.S. Pat. No. 5,939,130 describes a coating film forming method for forming a resist coating film on an upper surface of a wafer held by a spin chuck in a chamber.
Ahn et al., U.S. Pat. No. 6,522,385 describes an air shower head for an exposure device of photolithography equipment without chemical substances that could otherwise contaminate a photoresist layer on a semiconductor wafer and degrade the profile of the photoresist pattern.
The above-mentioned patents do not detect photoresist coating failures on a semiconductor wafer while simultaneously sensing a notch in the wafer.